The present invention relates generally to molded, plastic strain relief bushings. More particularly the present invention is related to two piece strain relief bushings which are folded together about a cord to be secured prior to installation in a suitable apertured work piece. It is believed that the invention is most properly classified in United States Class 174, Subclass 153.
In the prior art all known strain relief bushings of the two piece type comprise a relatively larger body portion which cooperates with a smaller friction block adapted to be snap fitted to the body. In many forms of prior art the friction block is integrally attached to the body by some form of hinge like strap structure so that both of the cooperating pieces are unitary. In other words, only once unitary piece exits from the mold during the manufacturing process, and only one part need be inventoried by the manufacturer or assembler. The two pieces are then folded together against yieldable tension from the connecting strap so as to appropriately align and insert the gripping block into the body portion about the electrical cord, for subsequent insertion into the previously established orifice in the work piece. Suitable frictional binding between integral internal parts and the outer insulation of the secured electrical cord is thus established, and the prior art in some instances provides for the creation of additional friction when axial pressure is placed upon the cord through the use of binding frictional serrations, grooves, recesses or the like.
U.S. Pat. Nos. 3,298,840 and more particularly 3,290,430 are typical of the latter structure. In these strain relief bushings the strap structure is generally flat, and it angularly extends between two pieces having their axis opposed by at least 90 degrees. As mentioned in Klumpp Pat. No. 3,290,430, in column 2, lines 7 through 20, for example, a fundamental object of such representative prior art is to avoid the use of hinge structure which had hitherto been a problem in "unitary" two piece strain relief bushings of that general type.
A wide variety of bushings adapted to prevent damage caused to an insulated electrical cable by unusual amounts of stress or strain are currently available and in use. However, as will be appreciated by those skilled in the assembly of electrical and electronic equipment, a number of yet unsolved problems are encountered with the installation and use of known strain relief bushings.
One major drawback of well-known strain relief bushings is that installation is cumbersome. Generally, the bushing must first be crimped into engagement with the insulating jacket of an electrical cord which has been inserted through a suitable mounting orifice. Then the bushing must be forced through the orifice until it comes into position in gripping engagement with the inner periphery of the orifice. Once the bushing is correctly positioned, its parts must be locked together to prevent displacement of the cord and the bushing from the mounting orifice. Finally, when a conventional compressive hand tool is employed to compress conventional strain relief bushing segments together, a rocking motion tends to become dynamically established at the point of internal tongue contact with the captured wire. Because of leverage, this motion tends to enlarge the width of the bushing front snout, and if deformation is extreme enough substantial resistance to orifice penetration may result.
It would therefore be desirable to provide a strain relief bushing which can be quickly and easily installed in gripping engagement with the insulating jacket of an electrical cord with a single hand motion. Moreover, it would be advantageous to provide a strain relief bushing of this type which is adapted to be loaded in the magazine of a hand-held pliers-like bushing assembly tool and installed in a single "shot" motion.
Another yet unsolved problem encountered with prior art strain relief bushings is the ineffective design of the strap or cord which connects interlocking sections of the bushing. The cords of bushings known to us are cumbersome and complicate installation of the bushing as well as subsequent access to the other electrical or electronic components of a particular system. Hence it would be most advantageous to provide an improved, streamlined, and flexible strap to connect interlocking portions of the strain relief bushing.
Also, well-known prior art strain relief bushings generally fail under unusual strain. Under tension of continued duration, the bushings known to us weaken, become distorted, and eventually pull away from the insulative jacket of the electrical cord and out of locking engagement with the mounting orifice. Thus it would be desirable to provide a strain relief bushing which is adapted to more securely engage the insulative jacket of the electrical cord when increased tension is applied to the cord.
One further problem yet unaddressed by prior art strain relief bushings is encountered where additional meshing is required to protect the electrical cord. The prior art bushings are not sufficiently flexible to fully encompass and effectively engage the wire with additional mesh insulation. Therefore it would be most desirable to provide a strain relief bushing which is adapted to fully encompass a wire with additional meshing protectors.
Numerous prior art patents exist for strain relief bushings employing two or more cooperative, interlocking parts. For example, U.S. Pat. No. 2,424,758 issued to Klumpp on July 29, 1947 teaches a two-piece, self-locking bushing which includes a body and a cooperating block portion which is adapted to be slidably fitted into the body after installation to prevent the cable from turning within its fitting. A plurality of fingers are provided to engage the collar of the two-piece snap bushing described by Klumpp in U.S. Pat. No. 4,137,602, issued Feb. 6, 1979. Other typical multi-part bushing construction is represented by U.S. Pat. No. 2,724,736, issued to Klumpp on Nov. 22, 1955 and Nicholson, U.S. Pat. No. 3,843,833, dated Oct. 22, 1974, which includes interior teeth or serrations adapted to grip the jacket of the electrical cord.
A variety of patents also exist for unitary strain relief bushings. For example, the bushings described by Klumpp in U.S. Pat. Nos. 2,424,756 and 2,424,757, issued on July 29, 1947, include a multiplicity of expanding fingers adapted to engage the wall plate after installation.
Among the various prior art patents which teach the use of a strap or tie to connect the cooperating parts of the bushing are: U.S. Pat. No. 2,930,840, issued to Klumpp on Mar. 29, 1960; U.S. Pat. No. 2,974,186, issued Mar. 7, 1961 to Klumpp; Klumpp, U.S. Pat. No. 3,290,430, issued Dec. 6, 1966; U.S. Pat. No. 3,689,014, issued to Fink on Sep. 5, 1972; Jemison, U.S. Pat. No. 3,749,818, issued July 31, 1973; and, U.S. Pat. No. 3,779,494, issued Dec. 18, 1973 to Nicholson.